Benchmark: Cache global vs reference

Tests:

use global
var value = 0; (function() { function run() { for (var i = 0; i < 10000; i++) { value = Math.min(value, Math.random()); } } run(); })();
cache global
var value = 0; (function() { var MathGlobal = Math; function run() { for (var i = 0; i < 10000; i++) { value = MathGlobal.min(value, MathGlobal.random()); } } run(); })();

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
use global
cache global

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 8 years ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.79 Safari/537.36 Edge/14.14393

Browser/OS: Chrome 51 on Windows

View result in a separate tab

Test name	Executions per second
use global	388.7 Ops/sec
cache global	1624.7 Ops/sec

Autogenerated LLM Summary (model llama3.2:3b, generated 2 months ago):

LLMs can make mistakes. Check important info.

I'll break down the provided benchmark and its options, pros, and cons.

**Benchmark Overview**

The test measures the performance difference between two approaches: using a global variable (`var value = 0;`) and caching the `Math` object in a local scope (`var MathGlobal = Math;`). The goal is to determine which approach has better cache locality, leading to improved performance.

**Options Compared**

There are two options compared:

1. **Use Global**: In this approach, a global variable `value` is declared, and then the `Math.min()` function is called with the global `value` as an argument.
2. **Cache Global**: In this approach, a local scope creates a variable `MathGlobal` that refers to the `Math` object, which is then used in the `Math.min()` function.

**Pros and Cons**

*   **Use Global (Option 1)**

*   Pros:
        *   Simpler code
        *   No need to create a new scope or context for the `Math` object.
    *   Cons:
        *   Poor cache locality, as the global variable is not optimized for caching in JavaScript engines.
*   **Cache Global (Option 2)**

*   Pros:

*   Better cache locality, as the local `MathGlobal` scope is more likely to be cached by the JavaScript engine.

*   More efficient performance
    *   Cons:
        *   Requires creating a new scope or context for the `Math` object.
        *   Code may appear more complex

**Library and Special JS Feature**

In both test cases, no libraries are used. However, they do utilize a special JavaScript feature:

*   **Lexical Scoping**: The test uses lexical scoping to create local variables (`value`, `MathGlobal`) within the scope of each benchmark function.

**Other Considerations**

The test assumes that the JavaScript engine being tested (e.g., V8 in Chrome) will cache the execution context for the local variable `value` or `MathGlobal`. This assumption is based on the behavior of modern JavaScript engines, which use a technique called **register-based caching** to optimize performance.

If not using these approaches, you can implement additional optimization techniques such as:

*   **Using native functions**: Consider replacing the global object calls with native functions that have optimized implementations.
*   **Minimizing scope creation**: Reduce the number of scopes created by reusing variables or using closures to share state between functions.
*   **Loop unrolling and optimizations**: Optimize loops for better performance, such as loop unrolling or using SIMD instructions (if supported).

Keep in mind that the effectiveness of these techniques depends on the specific JavaScript engine being used.

**Alternatives**

For measuring JavaScript performance and benchmarking:

1.  **Benchmark.js**: A popular tool for writing fast and accurate benchmarks.
2.  **V8 Benchmark Suite**: A collection of benchmark suites designed to test the performance of the V8 JavaScript engine.
3.  **jsPerf**: A web-based testing framework for comparing browser performances.

Each alternative has its strengths and weaknesses, so choose the one that best suits your specific use case and requirements.

Related benchmarks:

Cache global vs reference (version: 1)

Comparing performance of: use global vs cache global

Created: 8 years ago by: Registered User

Jump to the latest result

use global

cache global

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 2 months ago):